Extraction and Fractionation of Biopolymers and Resins from Plant Materials

ABSTRACT

A method for the extraction, separation, fractionation and purification of biopolymers from plant materials using supercritical and/or subcritical solvent extractions is disclosed. Specifically, the process can be used for the separation of resins and rubber from guayule shrub ( Parthenium argentatum ), and other rubber and/or resin containing plant materials, using supercritical solvent extraction, for example supercritical carbon dioxide extraction. Additionally, polar and/or non-polar co-solvents can be used with supercritical carbon dioxide to enhance the selective extraction of resins and rubbers from the shrub.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a divisional of and claims the benefit of priorityof U.S. application Ser. No. 11/327,266, filed Jan. 5, 2006, whichclaims the benefit of priority of U.S. Application Ser. No. 60/641,578,filed Jan. 5, 2005.

FIELD OF THE INVENTION

This invention relates in general to the extraction, separation,fractionation and purification of resins and biopolymers from plantmaterials using supercritical solvent extractions. Specifically, theinvention relates to a process for the separation of resins and rubberfrom the guayule shrub (Parthenium argentatum) using supercriticalsolvent extraction, for example, supercritical carbon dioxideextraction. Additionally, co-solvents can be used with supercriticalcarbon dioxide to enhance the selective extraction of resins and rubbersfrom the plant material. Finally, subcritical water extraction may alsobe used according to this invention.

BACKGROUND OF THE INVENTION

Guayule is a desert shrub native to the southwestern United States andnorthern Mexico and which produces polymeric isoprene essentiallyidentical to that made by Hevea rubber trees (e.g., Hevea brasiliensis)in Southeast Asia. As recently as 1910 it was the source of half of thenatural rubber used in the U.S. Since 1946, however, its use as a sourceof rubber has been all but abandoned in favor of cheaper Hevea rubberand synthetic rubbers. However, demand for natural rubber is expected toproduce shortages of that material in the future and rubber prices areexpected to rise significantly. Natural rubber having lower heathysteresis is required for many kinds of tires and amounts to about 35%of U.S. rubber use.

As an alternative to synthetic rubber sources, attention is beingdirected to the production of hydrocarbons in plants such as guayule(Parthenium argentatum). Guayule normally yields one half ton to one tonof rubber per acre in cultivation when, after two years, the entireplant is harvested and processed. Guayule plants store latex in tinyinclusions in the bark, making harvest of the outer fibrous layers, orbagasse, of the plant, desirable.

Using traditional techniques, as much as 95% of the available naturalrubber may be recovered from plant materials, using parboiling, whichcoagulates the latex in the cells, followed by a milling step in acaustic solution to release the rubber. This traditional process thencauses the milled bagasse to sink to the bottom of the processing vesseland allows resin to float to the surface for collection. Morespecifically, in traditional processes, resins from plant materials areobtained by solvent extraction with polar solvents such as alcohols,ketones, and esters. A commonly used solvent for extracting the guayuleresin is acetone. The resin is recovered from the solution byevaporating the solvent. The rubber from the shrub is generallyextracted using hydrocarbon solvents such as hexane, cyclohexane ortoluene. Such processes are normally very expensive and notenvironmentally friendly. A water floatation method has also been usedfor the extraction of rubber.

Further, using traditional methods of guayule processing, plant materialis prepared by initially grinding it into small particles. Generally,the entire plant is fed whole, that is, with the leaves thereon as wellas dirt or foreign debris, into a grinding apparatus, for example, ahammermill. The ground material can be flaked, that is, crushed, byadding to a two-roll mill or other conventional equipment, whichruptures the rubber-containing cells. The communited plants aresubjected to a resin-rubber solvent system. The solvent system containsone or more solvents which extract the resin as well as the rubber fromthe guayule-type shrub. Examples of single-solvent systems includehalogenated hydrocarbons having from 1 to 6 carbon atoms, such aschloroform, perchloroethylene, chlorobenzene, and the like; and aromatichydrocarbons and alkyl-substituted aromatic hydrocarbons having from 6to 12 carbon atoms, such as benzene, toluene, xylene, and the like.

This solvent system typically contains one or more polar resin solventsas well as one or more hydrocarbon rubber solvents. Typical polar resinsolvents include alcohols having from 1 to 8 carbon atoms, such asmethanol, ethanol, isopropanol and the like; esters having from 3 to 8carbon atoms such as the various formates, the various acetates and thelike; ketones having from 3 to 8 carbon atoms, such as acetone, methylethyl ketone, and the like. Typical non-polar hydrocarbon rubbersolvents include alkanes having from 4 to 10 carbon atoms, such aspentane, hexane, and the like; and cycloalkanes having from 5 to 15carbon atoms, such as cyclohexane, decalin, the various monoterpenes,and the like. Although the two types of solvents can form a two-phasesystem, they often form a single phase when utilized in properproportions. One manner of adding different type solvents to the shrubis separately, but simultaneously. However, they are generally preparedas a mixture and added as such.

Accordingly, numerous combinations of a polar resin solvent and ahydrocarbon rubber solvent can exist. A specific solvent system is anazeotropic composition of approximately 80% by weight of pentane, morespecifically 78.1% by weight, and 20% by weight of acetone, morespecifically 21.9% by weight. The ratio by weight of solvent to theamount of shredded shrub can be any amount sufficient to generallyextract most of the rubber and resin, as for example from about 1 partby weight of solvent up to about 20 parts by weight of solvent for each1 part by weight of shrub, and preferably about 3 parts by weight ofsolvent to 1 part by weight of shrub. The rubber-resin miscella soobtained typically contains about 1 to 25% by weight of total solids,that is resin plus rubber, and preferably about 9 to 18% by weight oftotal solids with the amount of resin by weight being from about 1 toabout 3 parts for every 1 part by weight of rubber.

Furthermore, traditional methods of plant processing have been hamperedby the use of these highly toxic compounds and cumbersome processes. Forexample, in prior industrial operations, hexane and heptane solventshave been used in the solvent extraction of oil-containing vegetablematter. The extraction apparatus typically includes vertical extractiontowers, screw extractors and bucket extractors. With current equipment,several extraction stages are necessary in order to circulate themiscella and attain sufficient wetting of the material to be extracted,thereby requiring the use of a higher proportion of solvent.

In addition, overall energy consumption inherent in previous slurryseparations has been excessive, if not prohibitive. Processing of thistype of plant material traditionally requires wetting to form a slurry,a high amount of heat, and a difficult separation of the solvent fromthe extracted oil and defatted meal. Complete removal of solvents, suchas hexane, from the spent botanical residue is practically impossible byconventional steam stripping techniques.

The method of using gaseous solvents at both supercritical andsubcritical conditions, such as carbon dioxide and propane, is alsoproblematic. In these systems, the operating pressure must exceed 125psi to remain in liquid state and even higher if temperatures areelevated. Because of the difficulties in working at high pressure,multiple extraction vessels are required, which limits the speed andefficiency of these extractions. Further, it is difficult to maintainpressures consistently, resulting in freezing, gumming, or poorseparation of the extracted materials, which may clog the system. Alsohydrolysis of lipids or inadequate processing may decrease the yield.

In an effort to overcome some of these difficulties, in recent yearscellulose degradation methods using enzymes such as pectin hydrolases,cellulose, alkalis, or acids have been taught. In addition, the priorart teaches a number of processes for production of glucose fromcellulose in the presence of lignin. Crushing and extraction processesfor hydrocarbon-containing plants have also been taught. However, priorart processes have not dealt with the problem of obtaining hydrocarbonsfrom hydrocarbon-containing plants wherein the hydrocarbon content islow and is contained in laticifer cells.

Additionally, traditional extraction methods make it difficult andinefficient to extract resins from plant materials, particularly fromthe bagasse. Bagasse is difficult to extract with hydrocarbon solventsfor several reasons. First, the compounds of interest are adhered in thebotanical matrix, so the material needs to be ground finely foraccessibility of the solvent to these compounds. Second, the compoundsof interest are significantly different in polarity, namely, resins arepolar and rubber is non-polar. This makes it difficult to utilize asingle solvent system, and therefore, most extraction processes utilizea two-solvent extraction system, e.g., acetone for resin extractionfollowed by cyclohexane for rubber extraction. Third, ground bagasse hasphysical properties that translate into very slow percolation rate forliquid solvents. Fourth, contact with oxygen can oxidize the rubberextract in other processes.

Thus, it has been difficult to design a commercially viable process forthe extraction of bagasse with liquid solvents. Additionally, due to theproblems with slow percolation rate through the bagasse, traditionalprocessing methods have resulted in a low commercial output, and much ofthe unused bagasse contains residual solvents. The residual solvents inthe remaining bagasse pose environmental safety hazards and make theexcess bagasse mostly unusable for other applications. Finally, the lowoutput makes these prior art extraction processes not commerciallyviable methods of extraction.

Therefore, a need exists for a cost-effective, efficient, andenvironmentally friendly method of extracting and fractionating rubberand resins from plant materials, such as guayule.

DETAILED DESCRIPTION OF THE INVENTION

The present invention utilizes supercritical solvents, such as carbondioxide, optionally in combination with other co-solvents, for theseparation, fractionation and purification of low molecular weightresins and high molecular weight biopolymers, such as rubber, from plantmaterials, such a guayule. One embodiment uses supercritical carbondioxide for the simultaneous extraction, separation, fractionation andpurification of rubber and resins from guayule plant materials.Alternate embodiments of the present invention comprise the steps ofresin and rubber extraction with supercritical carbon dioxide,separation, fractionation and purification of rubber and resins insuccession rather than simultaneously.

As disclosed herein, the present invention is a method of extractinghigh molecular weight biopolymers, for example, rubber, and resin fromplant material using supercritical fluid at medium to high pressures. Inat least one embodiment, carbon dioxide gas is compressed into a denseliquid, this liquid is then pumped into a cylindrically-shapedhigh-pressure vessel containing the guayule shrub, the extract ladenliquid is then pumped into a separation chamber, where the extract isseparated from the gas, and the gas is recovered for reuse. Manyvariations of these processes and conditions, as disclosed herein, canbe used including different co-solvent systems and methods of plantmaterial preparation. These will be apparent to those skilled in therelevant art.

While supercritical fluid extraction processes have been usedcommercially for the extraction of alkaloids, flavor components,perfumes and the like, for the reasons articulated above, this processpreviously has not been shown to be effective or useful in extractinghigh molecular weight biopolymers from plant materials as complex asguayule, which contain thousands of secondary products.

Rubber is a naturally-occurring hydrocarbon polymer ofcis-1,4-polyisoprene with 400-50,000 isoprene monomeric unitsenzymatically linked in a head-to-tail configuration. It is to beunderstood that the rubbers from numerous plants, such as guayuleplants, are defined herein as “guayule type” rubbers and hence can beutilized either alone or in combination with each other. Hereinafterwhenever reference is made to guayule plants or shrubs, it is to beunderstood that the below-described plants and shrubs can also beutilized.

Guayule-type plants which can be utilized to prepare rubber-containingmiscellae include guayule, gopher plant (Euphorbia lathyris), mariola(Parthenium incanum), rabbitbrush (Chrysothanmus nauseosus), candelilla(Pedilanthus macrocarpus), Madagascar rubbervine (Cryptostegiagrandiflora), milkweeds (Asclepias syriaca, speciosa, subulata, et al.),goldenrods (Solidago altissima, graminifolia, rigida, et al.), Russiandandelion (Taraxacum kok-saghyz), mountain mint (Pycnanthemum incanum),American germander (Teucreum canadense), and tall bellflower (Campanulaamericana). Many other plants which produce rubber and rubber-likehydrocarbons are known, particularly among the Asteraceae (Compositae),Euphorbiaceae, Campanulaceae, Labiatae, and Moraceae families, and hencecan be utilized.

Plant materials may be obtained using a variety of conventional andexperimental harvesting processes. Generally, plants are cultivated,harvested and bailed using standard farming practices. Various portionsof a plant may be used to obtain plant materials, including leaves,bark, stems, root systems or root balls.

The plant need not be de-leafed because the metal ions such asmanganese, iron and copper in the leaves that could promote oxidativedegradation of the rubber are not extracted into the rubber solvents.Further, processing the plant, including the leaves, may add to thequality of the bagasse because the leaves contain mineral, nitrogenousand carbohydrate components that could enhance the quality of thebagasse for certain post-processing applications. Further, in thisembodiment of the invention, the process results in three products:total shrub rubber, total shrub resin and total shrub bagasse.

The plants may be processed by de-leafing or de-barking using mechanizedshearing or hand shearing, or may be processed with leaves and washedwithout de-leafing or de-barking. Removal of the leaves from theharvested shrub prior to the disclosed supercritical extraction processwould permit the leaf wax to be isolated and sold separately.Defoliation will also eliminate the wax as a possible contaminant in theresin and rubber solvents.

Initial processing of plant materials may consist of a high pressurewater system to strip the bark or leaves off the plant. Plant materialsmay be processed at a processing facility by conveyor, and any leftoverplant material transported away for further refining or disposal.Secondary processing prior to extraction may further comprise grinding,hammermilling, or forcibly fractionating whole or partial plantmaterials into smaller pieces. The plant material may also be ground andthen pelleted. Plant material may also be pre-treated by enzymaticdegradation of either whole or partial plants. Optionally, the bagassemay then be further extracted according to the methods disclosed herein.

The extraction process disclosed herein can be carried out on a largescale using industrial extraction equipment, or on a small scale usingtypical laboratory scale units such as the Spe-ed SFE-2 from AppliedSeparations, 930 Hamilton Street, Allentown, Pa., 18101.

In the supercritical state, solvents, or supercritical fluids (SCFs),can readily penetrate porous and fibrous materials, and are particularlywell adapted to processing guayule plant materials. Since the solvatingpowers can be adjusted by changing the pressure or temperature,separation and fractionation of resins and rubber is fast and easy. Inaddition, fractionation can be improved and extraction enhanced for highmolecular weight components by adding modifiers or co-solvents, makingSCFs a highly-versatile solvent to utilize with improvedseparation/fractionation capabilities when compared to conventionalorganic liquid solvent extraction processes.

Generally, SCFs are fluids that exist at the transition between liquidsand gases, and share some qualities of each. A pure SCF is any compoundat a temperature and pressure above the critical values (e.g., a fluidis termed ‘super-critical’ when the temperature and the pressure exceedthe critical pressure point of a vapor-liquid coexistence curve). Morespecifically, a fluid is termed supercritical when the temperature andpressure are higher than the corresponding critical values. The criticaltemperature of a fluid is the temperature above which liquefaction isnot possible at any pressure.

Critical pressure (“CP”) is further defined as the pressure required toliquefy a gas at the critical temperature. At temperatures and pressuresabove those at the critical point, fluids are at supercriticalconditions. A supercritical fluid is characterized by physical andthermal properties that are between those of the gas and pure liquid.The fluid density is a strong function of the temperature and pressure.Above the critical temperature of a compound, the pure gaseous componentcannot be liquefied regardless of the pressure applied. The CP is thevapor pressure of the gas at the critical temperature. In thesupercritical state, only one phase exists. This phase retains solventpower approximating liquids as well as the transport properties commonto gases.

For example a comparison of typical values for density, viscosity, anddiffusivity of gases, liquids and SCFs is as follows: TABLE 1 Comparisonof physical and transport properties of gases, liquids and SCFs.Property Density (kg/m3) Viscosity (cP) Diffusivity (mm2/s) Gas 1 0.01 1-10 SCF 100-800 0.05-0.1  0.01-0.1 Liquid 1000 0.5-1.0 0.001

It is noted that pressure and temperature may be manipulated using acombination of isobaric changes in temperature with isothermal changesin pressure. Using SCFs, it is possible to convert a pure component froma liquid to a gas (and vice versa) via the supercritical region withoutincurring a phase transition. The behavior of a fluid in thesupercritical state can be described as that of a very mobile liquid,and the solubility behavior approaches that of the liquid phase whilepenetration into a solid matrix is facilitated by the gas-like transportproperties.

As a result, the rates of extraction and phase separation can besignificantly faster than for conventional extraction process, andextraction conditions can be controlled much better to further optimizeseparation. SCF extraction is known to be dependent on the density ofthe fluid, which in turn may be manipulated through control of thesystem pressure and temperature. Further, the dissolving power of SCFincreases with isothermal increase in density or an isopyonic (i.e.,constant density) increase in temperature.

Under thermodynamic equilibrium conditions, the visual distinctionbetween liquid and gas phases, as well as the difference between liquidand gas densities disappear at and above the critical point. Similardrastic changes exist in properties of a liquid mixture as it approachesthe thermodynamic critical loci of the mixture. This provides the moregas-like physical properties of SCF, including thermal conductivity,surface tension, constant-pressure heat capacity and viscosity, whichare far superior to standard liquids to enchance mass transfer duringextraction. For example, if comparing a liquid organic solvent with asupercritical fluid solvent with the same density, the thermalconductivity and diffusity of a SCF are higher and the viscosity is muchlower. Furthermore, with SCFs, surface tension and heat of vaporizationhave almost completely disappeared.

Supercritical fluids are an alternative to organic solvents inindustrial purification and re-crystallization operations, because theyprovide a more environmentally-friendly process and eliminate some ofthe dangers to workers that are associated with traditional organicmethods. SCF-based extraction processes do not produce the VOC and ODCemissions that are the by-products of traditional organic processes.Supercritical fluids are commonly used to extract analytes from samples.

For example, supercritical fluid extraction (SFE) processes are commonlyused in the food industry, e.g., for coffee and tea decaffeination andfor beer brewing. SCF processes are also used in polymer,pharmaceutical, lubricant, and fine chemical industries and are valuedfor their potential to increase product performance levels overtraditional processing technologies. In addition, SCFs are used in therecovery of organics from oil shale, separations of biological fluids,bio-separation, petroleum recovery, crude de-asphalting and de-waxing,coal processing, selective extraction of fragrances, oils andimpurities, pollution control, and combustion.

Supercritical fluids provide the advantage that they are inexpensive,extract the analytes faster and are more environmentally friendly thanorganic solvents. For example, SCFs have solvating powers similar toliquid organic solvents but with higher diffusivities, lower viscosity,and lower surface tension. The solvating power can also be adjustedeasily by changing the pressure or temperature for efficient separationof analytes. According to one embodiment, carbon dioxide is used as thesupercritical solvent. Alternately, other supercritical solvents arealso used, including, but not limited to, ammonia, water, nitrous oxide,xenon, krypton, methane, ethane, ethylene, propylene, propane, pentane,methanol, ethanol, isopropanol, isobutanol, chlorotrifluoromethane,monofluoromethane, cyclohexanol, toluene and other solvents known in theart.

Supercritical fluid carbon dioxide has the gas-like physical propertiesof very low surface tension, low viscosity and high diffusivity, whichallow a supercritical fluid solvent to penetrate an ultra low porositysubstrate, such as a bed of finely ground bagasse, in a fixed bedextractor vessel and dissolve the compounds of interest. Supercriticalcarbon dioxide appears to have sufficient polarity at medium to highpressures and temperatures to be an adequate solvent of the resinousmaterials (but is a poor solvent for the rubber). Finally, supercriticalcarbon dioxide, because of its low surface tension, low viscosity andhigh diffusivity, can penetrate the bed of ground bagasse at a very highpercolation rate, which allows for a very quick extraction when comparedto hydrocarbon solvents. Using supercritical CO₂ is advantageous overother extraction methods and has the potential to be the superiorprocess for resin and rubber extraction on a commercial scale.

Following initial processing of plant material, described in more detailbelow, the plant material is contacted with carbon dioxide near or abovethe supercritical conditions for a sufficient time to solubilize theresin and/or rubber components, forming a supercritical solution. Aswill be disclosed more fully herein, this is followed by a collectionprocess in which the resins and rubber, which precipitate out from thesupercritical solution, are collected when the pressure is reduced toatmospheric level. The pressures used for extraction can range fromabout 1,500 psi to about 10,000 psi, depending on the temperature, forthe supercritical carbon dioxide and for the carbon dioxide withmodifier co-solvent systems.

In another embodiment, the guayule shrub is first extracted withsupercritical carbon dioxide at high temperatures and pressures and thetemperature and pressure conditions are lowered or changed toprecipitate the various insoluble fractions. In yet another embodiment,fractionation can be carried out by extracting guayule shrub atdifferent temperatures and pressures, going from low to high, andcollecting each fraction, a novel way to make different melting pointresins. Preferably, this method of extraction can be used to fractionatethe resins and rubber in a single system and with a single solvent.

The steps of the disclosed method are capable of being performed invarious orders or, in some cases, as noted, at approximately the sametime. For example, in one embodiment, simultaneous extraction of resinand rubber using a non-polar co-solvent is followed by fractionation ina supercritical fluid system, for example, using supercritical CO₂, intoa rubber fraction and a resin fraction.

More specifically, the present invention discloses a method of rubberand resin extraction in at least the following alternate andnon-limiting ways: (1) approximately simultaneous extraction of rubberand resin using a supercritical solvent, such as supercritical CO₂without use of any co-solvents; (2) approximately simultaneousextraction of resin and rubber using a non-polar co-solvent, followed byfractionation in a supercritical fluid system, for example, usingsupercritical CO₂, into a rubber fraction and a resin fraction; or (3)high pressure supercritical fluid extraction at a specific narrow rangeof pressure and temperatures to remove the resin, followed by a highpressure solvent extraction in the same vessel, with cyclohexane orsimilar non-polar solvent to remove the rubber; or (4) high pressuresolvent extraction at a specific range of temperature and pressure withcyclohexane or similar non-polar solvent to remove the rubber, followedby high pressure supercritical fluid extraction at a specific narrowrange of pressure and temperatures to remove the resin.

Each of the above alternate embodiments of the disclosed methods is theneach optionally followed by a final rinse of supercritical carbondioxide to remove the residual solvent from the bagasse.

Referring now to the embodiment of the disclosed method comprisingsimultaneous extraction of rubber and resin, the method comprises asimultaneous resin and rubber extraction utilizing supercritical carbondioxide at specific pressure, preferably between 1,500 and 10,000 psi,and more preferably between 5,000 and 10,000 psi, with a temperaturerange between 60-100° C. An alternate embodiment further includes usinga non-polar co-solvent, preferably at a co-solvent ratio 3-10 times thefeedstock weight, in order to simultaneously extract the resins and therubber. According to the present disclosure non-polar co-solventsinclude, but are not limited to, hexane, hexene, octane, pentane,cyclohexane, iso-octane, and 1-hexene. Another embodiment alternatelyincludes using a polar co-solvent, for example, water, ethanol, methanoland acetone. Additionally, the present disclosure includes asupercritical fluid extraction further including both a polar co-solventand a non-polar co-solvent.

The simultaneous extraction is followed by a fractionation step,utilizing a supercritical fluid system to fractionate the material intoa rubber fraction and a resin fraction. The fractionation is thenfollowed by a rinse of pure carbon dioxide, which removes the residualsolvent from the bagasse.

In an alternate embodiment, high pressure supercritical fluid extractionat a specific narrow range of pressure and temperatures to remove theresin is followed by a high pressure solvent extraction in the samevessel, with a non-polar solvent to remove the rubber. In anotherembodiment, high pressure solvent extraction is carried out at aspecific range of temperature and pressure with cyclohexane or similarnon-polar solvent to remove the rubber, followed by high pressuresupercritical fluid extraction at a specific narrow range of pressureand temperatures to remove the resin. In yet another embodiment, one ormore of the above processes are then optionally followed by a finalrinse of supercritical carbon dioxide to remove the residual solventfrom the bagasse.

The removal of the resins and the second extraction is performed underpressure, which allows circumvention of the slow percolation problem,and provides a method capable of obtaining a high yield of rubber fromthe product. The final rinse with carbon dioxide allows for eliminationof the environmental problem. Another version of this second processutilizes a polar solvent that is selective for resin such as alcohol oracetone to accelerate the removal of the resin and in some cases tosuppress the extraction of the rubber for an even higher yield andpurity of resin and rubber fraction.

The present disclosure also envisions the use of subcritical liquid forthe extraction process. Many variations of these process and conditionscan be used such as different co-solvent systems, subcritical conditionsto extract low molecular weight fractions, and the like, and these willbe apparent to those skilled in the art. Specifically though, thesubcritical method comprises contacting plant material with a compressedgas solvent, wherein the temperature and pressure of the solvent are atsubcritical liquid conditions; maintaining the subcritical liquid for asufficient time, wherein the biopolymer and the solvent form asubcritical liquid solvent solution; and extracting the biopolymer bypercolation of the subcritical liquid through a bed of the plantmaterial utilizing an inert percolation aid such as diatomaceous earth.

As an additional alternate step, plant material is stored prior toprocessing. Specifically, a presoaking process is used prior to thesupercritical extraction. In this embodiment, storage comprises mixingthe material in communited form with at least one essentially water-freeorganic liquid to form a slurry in which the material is protected fromcontact with oxygen and then storing said slurry for at least 24 hours.In this embodiment, the organic liquid may be selected from (1)alcohols, ethers, esters and ketones having one to eight carbon atoms;(2) hydrocarbon solvents having a boiling range within about 20°-100°C.; (3) concentrated resin miscella; (4) hydrocarbon/guayulerubber/guayule resin miscella; (5) hydrocarbon/guayule rubber miscellacomprising said hydrocarbon solvent and about 2-4% guayule rubber, or(6) mixtures thereof. In this embodiment, the liquid is acetone oracetone/resin miscella and contains a stabilizer such as apara-phenylenediamine stabilizer.

Additionally, the storage of the plant material may comprise the entirenon-defoliated plant and may be dried to a moisture content of about5-25% before forming the slurry. In some embodiments, the slurry issubjected to mild agitation. This storage method prevents development ofoffensive odors, due to the degradation, as well as prevents microfloralgrowth on the shrub. This method also allows communited guayule/organicsolvent slurry to be pumped from one processing unit to another,avoiding undue exposure of the material to air. In addition, theinvention permits partial or essentially complete extraction of usefulproducts from the shrub during storage, thus reducing costs, time andequipment required.

Another alternate additional step is pretreatment of the plant materialto increase the efficiency of the supercritical extraction processand/or increase the yield of rubber and resin produced in theextraction. In one embodiment of the present invention, the pretreatmentstep comprises the application of a guanidine salt solution to the plantmaterial, to soften the plant cell tissue and denature the protein coatthat surrounds each globule of rubber, in order to facilitate therelease of rubber into solution.

Once the rubber and resin have been extracted, the bagasse recoveredfrom the solvent extraction process is relatively free of water andcould be used as a fuel to supply the power requirements of thedisclosed system and method, or as a separate marketable product.Alternatively, complete hydrolysis of the bagasse can be affected tofermentable sugars, which could be used as such, or fermented to prepareethanol.

The resins which are extracted from the shrub are also recoverable andare a mixture of terpenes, terpenoids, parthenoids and glycerides offatty acids. The resin component also contains a valuable hard waxsimilar to carnauba wax. The resins can be used as an adhesive inplywood and as a component in varnishes. Further, resin can also be usedas a tackifying resin in the manufacture of reinforced composite rubberarticles such as tires and car radiator hoses.

EXAMPLES

The process of extraction of resins and rubber is explained in thefollowing examples; the examples set forth herein below are to beunderstood as not limiting the disclosure. Examples 1-15 disclosedherein are performed according to one or more embodiments of thedisclosed method. The results of these experiments illustrate theadvantages of using the disclosed supercritical extraction method. Inorder to measure and analyze the rubber and resin extracts, the ASE(accelerated solvent extraction) method is used to measure the percentrubber and resin extracted using supercritical solvent extractionaccording to the present disclosure.

The ASE system used for determining rubber and resin extracted using thedisclosed method comprises the following: a polypropylene centrifugetube, 50 ml, with skirt; aluminum weighing dish, 70 mm diameter, withtab; a drying oven, Thelco Model 130DM (or equivalent); a centrifuge,Dynac Model 420101 (or equivalent); an analytical balance, MettlerToledo AG 104 (or equivalent) with resolution of 0.01 mg; a vacuum oven,VWR Model 1400E (or equivalent); and an Accelerated Solvent Extractor(A.S.E.), Dionex Model 200 with solvent controller; extraction cells, 11ml with filter discs; Borosillicate vials, 40 ml, with septa and lids;and a coffee grinder. Further, according to one embodiment, thefollowing reagents are used: acetone; cyclohexane, methyl alcohol;nitrogen; and Ottawa sand.

The analysis of the extract begins by placing the plant material, suchas the whole guayule shrub or coarsely or finely ground guayule shrub,in a supercritical fluid extraction (SFE) pressure vessel. In oneembodiment of the invention, the guayule shrub is chopped into smallpieces. In an alternate embodiment, the guayule shrub is shredded orfinely ground first.

Specifically, the sample of plant material is prepared by weighing theentire fresh sample and then cutting the branch tissue into 2 cmlengths. The plant material is also reduced through a chipper using a ⅜″round-hole screen to achieve the same particle size. Once reduced insize, the plant material is again weighed. The plant material is thendried in a suitable oven at 80° C. Once dried, the plant material isagain weighed. Next, the plant material is ground in a coffee grinder orother suitable apparatus. Then, the sample material is stored in jars orvials in a refrigerator.

The analysis is performed according to the following method. First, a1.5 g prepared plant material sample is placed into a tared aluminumdish. Second, another dish and a centrifuge tube are weighed for eachsample. Third, sand (approximately 2.5-3 g) is mixed with the sample,transferred to a cell (screw on bottom, place a filter inside), andscrew on top of cell. Additional sand is added to fill. The top andbottom are checked for tightness to prevent the run from aborting due tosolvent leak.

The cell is then loaded into top tray of ASE. A “blank” cell (filledwith only sand) is then loaded in the first position. The labeled vialsare then loaded into bottom tray and empty vials are placed in the R1-R4positions. The system is checked to verify that there is enough solventin the bottles. The gas is turned on followed by the ASE.

For the examples below, the following program schedule comprises threecycles of 20 minutes each with an oven temperature at 140° C. A 100%methyl alcohol flush is used with a 60 second purge and a 50%acetone/50% cyclohexane rinse. The samples are then loaded and the runis started. The vials are placed into a freezer until ready tocentrifuge. The vials are shaken gently (not stirred). About 20 ml ofthe sample mixture is poured or pipetted into the centrifuge tube and anequal amount of methyl alcohol is added. The vial is capped and iscentrifuged at 3,500 rpm for 20 minutes.

Following centrifugation, all but about 5 ml of supernatant is poured orpipetted off into the aluminum pan. The remainder of extract is added tothe tube. The vial is rinsed with 5 ml cyclohexane, and the rinse isadded to the tube. The vial is then rinsed with 5 ml acetone, and thatrinse is also added to the tube. Finally, an equal amount of methylalcohol is added to the centrifuge tube. The tube is then capped andcentrifuged at 3,500 rpm for 20 minutes.

Following this centrifugation, all supernatant is poured off into thepan, and the pan and the tube are left to dry in the hood. The dry panis then placed in a vacuum oven at 60° C. for 30 minutes. The pan andtube are then weighed and the percent resin and rubber are calculatedusing the following formulas: $\begin{matrix}{{\%\quad{Resin}} = {\frac{{Dried}\quad{{wt}.\quad{of}}\quad{Acetone}\quad{extract}}{{Sample}\quad{{wt}.}} \times 100}} & {{Formula}\quad 1} \\{{\%\quad{Rubber}} = {\frac{{Dried}\quad{{wt}.\quad{of}}\quad{Cyclohexane}\quad{extract}}{{Sample}\quad{{wt}.}} \times 100}} & {{Formula}\quad 2}\end{matrix}$

The following is a sample calculation illustrating use of the aboverubber and resin formulas: A) Sample weight 1.4919 g B) Al dish tare wt.for acetone extraction 2.2214 g C) Al dish + extracted residue 2.3304 gD) Acetone residue wt. = (C − B) 0.1090 g E) Tube tare wt. forcyclohexane extraction 11.2777 g  F) Tube + extracted residue 11.3118 g G) (Cyclo)hexane residue wt. = (F − E) 0.0341 g

$\begin{matrix}{{\%\quad{Resin}} = {{\frac{0.1090\quad g}{1.4919\quad g} \times 100} = {7.31\%}}} & {{Formula}\quad 1} \\{{\%\quad{Rubber}} = {{\frac{0.0341\quad g}{1.4919\quad g} \times 100} = {2.29\%}}} & {{Formula}\quad 2}\end{matrix}$

Example 1 50 ml Extraction of Natural Rubber with Pure CO₂ (5,000 psi,60° C.)

12.78 g of guayule shrub feedstock is placed in a 50 ml extractionvessel and extracted with pure carbon dioxide at a pressure of 5,000 psiand a temperature of 60° C. The flow rate is 3 liters/minute. Theextraction time is thirty minutes. A total of 0.37 g of solid yellowmaterial is extracted (2.89% of feedstock), plus an additional 0.06 gaccumulated in the cold trap. Supercritical carbon dioxide at theseprocessing conditions shows high selectivity for resin. The extractsample has a resin concentration in the CO₂ of 37.04% and is among thehighest of all the samples submitted. However the yield at 2.89% offeedstock is much lower than higher pressure and temperature samples.The percentage of rubber in the extract is 2.77% of the feedstock, whichis a high value for organic non-polar co-solvents.

Example 2 50 ml Extraction with Hexane Co-Solvent (9,800 psi, 100° C.)

15.05 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 60 g of hexane co-solvent at apressure of 9,800 psi and a temperature of 100° C. The flow rate is 3liters/minute. The time of extraction is twenty-three minutes. 1.21 g ofdark green film is extracted (8.04% of feedstock). An additional 1.41 gof primarily hexane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows the best extractioncapability for rubber when compared to all the other previousexperiments.

The extract sample has a resin concentration in the CO₂ of 16.20% and isamong the lowest concentration of resin; however, the yield at 8.04% offeedstock is higher than previous experiments. The percentage of rubberin the extract is 4.98% of the feedstock. These process conditionsindicate that the presence of relatively low concentration of hexaneco-solvent appears to promote the extraction of rubber. The analysis ofthe residue shows that the concentration of residual resin is 2.2% usingthe ASE method, and the concentration of rubber in the residue is 1.8%.This example illustrates the increased rubber yield using the disclosedsupercritical solvent extraction method including a non-polar solvent.

Example 3 50 ml Extraction with Hexane Co-Solvent (5,000 psi, 100° C.)

15.00 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 110 g of hexane co-solvent at apressure of 5,000 psi and a temperature of 100° C. The flow rate is 3liters/minute. The extraction is run for forty-five minutes. 0.71 g ofdark green film is extracted (4.73% of feedstock). An additional 14.89 gof primarily hexane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows good extraction capabilityfor rubber. The extract sample has a low resin concentration of 15.44%and a high yield of 4.73% feedstock. The percentage of rubber in theextract is 9.40% of the feedstock. These process conditions indicatethat the presence of relatively high concentration of hexane co-solventpromote the extraction of rubber and slightly increase the extraction ofresin. Using the ASE method, the analysis of the residue shows that theconcentration of residual resin is 2.0%, and the concentration of rubberin the residue is 0.8%. This example further illustrates the increasedrubber yield using one embodiment of the disclosed method, namelysupercritical solvent extraction including a non-polar co-solvent.

Example 4 50 ml Extraction with Hexane Co-Solvent (9,800 psi, 102° C.)

13.88 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 100 g of hexane co-solvent at apressure of 9,800 psi and a temperature of 102° C. The flow rate is 3liters/minute. The extraction is run for fifteen minutes. 0.71 g of darkgreen film is extracted (5.12% of feedstock). An additional 7.38 g ofprimarily hexane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows very good selectivity forrubber. The extract sample has a 16.81% concentration of resin, however,the feedstock yield of 5.12% is high. The percentage of rubber in theextract is 14.63% of the feedstock, which is relatively high, showingthat rubber is extractable at these process conditions. These processconditions indicate that the presence of hexane co-solvent promotes theextraction of rubber. Using the ASE method, the residue has a 2.1%concentration of resin and a 1.1% concentration of rubber.

Example 5 50 ml Extraction with Hexane Co-Solvent (9,900 psi, 80° C.)

12.98 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 115.38 g of hexane co-solvent at apressure of 9,900 psi and a temperature of 80° C. The flow rate is 3liters/minute. The extraction is run for thirty minutes. 0.60 g of darkgreen film is extracted (4.62% of feedstock). An additional 0.26 g ofprimarily hexane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows very good selectivity forrubber. The extract sample has a 12.35% concentration of resin and a4.62% yield of feedstock. The percentage of rubber in the extract is8.97% of the feedstock and indicates that rubber is extractable at theseprocess conditions. These process conditions further indicate that thepresence of hexane co-solvent promotes the extraction of rubber. Usingthe ASE method, the residue has a 2.3% concentration of resin and a 1.1%concentration of rubber.

Example 6 50 ml Extraction with Hexane Co-Solvent (9,800 psi, 80° C.)

13.10 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 110.16 g of hexane co-solvent at apressure of 9,800 psi and a temperature of 80° C. The flow rate is 3liters/minute. The extraction is run for one hour. 1.47 g of dark greenfilm is extracted (11.22% of feedstock). An additional 0.14 g ofprimarily hexane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows very good selectivity forrubber. The extract sample has a combined average resin concentration ofslightly less than 10% and an 11.22% yield of feedstock. The percentageof rubber in the extract is 10.5% of the feedstock, indicating thatrubber is highly extractable at these process conditions. These processconditions indicate that the presence of hexane co-solvent appears topromote the extraction of rubber. Using the ASE method, the residue hasa 2.0% concentration of resin and a 0.8% concentration of rubber.

Example 7 50 ml Extraction with 1-Hexene Co-Solvent (9,800 psi, 100° C.)

13.00 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 114.16 g of 1-hexene co-solvent at apressure of 9,800 psi and a temperature of 100° C. The flow rate is 3liters/minute. The extraction is run for one hour. 0.68 g of dark greenfilm is extracted (5.85% of feedstock). An additional 0.44 g ofprimarily hexene is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows very good selectivity forrubber. The extract sample has a combined average resin concentration of11.4% and a 5.85% feedstock yield. The percentage of rubber in theextract is 13.4% of the feedstock, indicating that rubber is highlyextractable at these process conditions. These process conditionsindicate that the presence of 1-hexene co-solvent promotes theextraction of rubber. Using the ASE method, the residue has a 2.0%concentration of resin and a 1.1% concentration of rubber.

Example 8 50 ml Extraction with Cyclohexane Co-Solvent (9,500 psi, 100°C.)

13.00 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 109.80 g of cylohexane co-solvent at apressure of 9,500 psi and a temperature of 100° C. The flow rate is 3liters/minute. The extraction is run for one hour. 0.81 g of dark greenfilm is extracted (6.23% of feedstock). An additional 0.40 g ofprimarily cyclohexane is collected in the cold trap. Supercriticalcarbon dioxide at these processing conditions shows very goodselectivity for resin. The extract sample has a combined average resinconcentration of 30.1% and a 6.23% yield of feedstock. The percentage ofrubber in the extract is 7.8% of the feedstock, indicating that bothresin and rubber are extractable at these process conditions. Using theASE method, the residue has a 3.0% concentration of resin and a 3.9%concentration of rubber.

Example 9 50 ml Extraction with Iso-Octane Co-Solvent (9,500 psi, 100°C.)

13.00 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 110.26 g of iso-octane co-solvent at apressure of 9,500 psi and a temperature of 100° C. The flow rate is 3liters/minute. The extraction is run for one hour. 0.71 of dark greenfilm is extracted (5.46% of feedstock). An additional 0.17 g ofprimarily iso-octane is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows good selectivity for resin.The extract sample of >30.1% resin is high, as is the total yield offeedstock at 5.46%. The percentage of rubber in the extract is 3.9% ofthe feedstock, which was moderate compared to most other organicnon-polar co-solvent experiments, indicating that iso-octane is not asefficacious a co-solvent for extracting rubber as hexane, 1-hexene, orcyclohexane. Using the ASE method, the residue has a 2.5% concentrationof resin and a 4.5% concentration of rubber.

Example 10 50 ml Extraction with Water Co-Solvent, (9,800 psi, 100° C.)

14.72 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 7.32 g of water co-solvent at apressure of 9,800 psi and a temperature of 100° C. The flow rate is 3liters/minute. The time of extraction is thirty minutes. 0.59 g ofprimarily solid yellow material is extracted (4.00% of feedstock), andan additional 0.16 g is collected in the cold trap. Supercritical carbondioxide at these processing conditions shows high selectivity forresins. The extract sample has a 39.59% concentration of resin,indicating that water promotes the extraction of resin, and a yield of4.00% of feedstock.

However, the percentage of rubber in the extract is only 0.83% of thefeedstock. These process conditions show a very high selectivity forresin and a relatively low selectivity for rubber, indicating thepresence of water promotes the extraction of resin and depresses theextraction of rubber. These process conditions are suitable for atwo-step commercial process that selectively extracts resin and leavesbehind the rubber for subsequent extract. The material in the cold trapis much lower in resin and rubber concentration than in the collectionvessel. Using the ASE method, the residue has a 2.3% concentration ofresin, and a 5.7% concentration of rubber.

Example 11 50 ml Extraction with Water Co-Solvent, (5,000 psi, 60° C.)

16.26 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 8.07 g of water co-solvent at apressure of 5,000 psi and a temperature of 60° C. The flow rate is 3liters/minute. The time of extraction is 24 minutes. 0.68 g of primarilysolid yellow material is extracted (4.18% of feedstock), and anadditional 0.13 g is collected in the cold trap. The extract sample at28.8% concentration of resin is not nearly as high as the previousexperiment which is performed at a higher pressure and temperature. Theyield at 4.18% of feedstock is among the highest.

However, the percentage of rubber in the extract is reported at only0.37% of the feedstock which is among the lowest amount when compared toother process conditions. These process conditions show that thepresence of water suppresses the extraction of the rubber, but that thehigher pressure conditions are more conducive for the extraction ofresin. The material in the cold trap has extremely low concentrations ofresin and rubber compared to that in the collection vessel. Using theASE method, the residue had a 2.6% concentration of resin, and a 5.8%concentration of rubber.

Example 12 50 ml Liquid Carbon Dioxide Extraction, (2,000 psi, 9.2° C.)

16.1 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide at a pressure of 2,000 psi and atemperature of 9.2° C. The extract vessel and pre-heater vessel are bothplaced in a container with ice to perform a cold extraction, however, weare unable to achieve flow and no extract is collected. The guayulefeedstock, at least at the particle size at which the test wasperformed, does not have an adequate percolation rate to perform theextraction. The slow percolation rate of the liquid carbon dioxidecauses the bed to compress and form a plug, which prevents extraction.Liquid carbon dioxide requires the use of a specialized extractor,pelletizing of the feedstock, or a much larger particle size, in orderfor this liquid carbon dioxide process to work effectively.

Example 13 50 ml Extraction with Ethanol Co-Solvent, (7,250 psi, 80° C.)

15.04 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 15 g of ethanol co-solvent at apressure of 7,250 psi and a temperature of 80° C. The flow rate is 3liters/minute. The time of extraction is 45 minutes. 0.58 g of solidyellow material and dark green film is extracted (3.85% of feedstock).Supercritical carbon dioxide at these processing conditions showsaverage selectivity for resins. The extract sample at 30.09%concentration of resin is not as high as other experiments. The yield at3.85% of feedstock is not as high as other process conditions utilizinghigher pressure or water and other co-solvents.

However, the percentage of rubber in the extract is reported at 0.51% ofthe feedstock, which is extremely low, indicating that the presence ofethanol suppresses the extraction of rubber. These process conditionsare suboptimal for a process designed to extract both resin and rubber,but the presence of ethanol may be beneficial for a single step processto extract a purified resin product. Using the ASE method, the residuehas a 2.6% concentration of resin, and a 5.4% concentration of rubber.

Example 14 50 ml Extraction with Acetone Co-Solvent, (5,000 psi, 60° C.)

15.06 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 15 g of acetone co-solvent at apressure of 5,000 psi and a temperature of 60° C. The flow rate is 3liters/minute. The time of extraction is 45 minutes. 0.63 g of darkgreen film is extracted (4.18% of feedstock). Supercritical carbondioxide at these processing conditions showed extraordinary selectivityfor resins. The extract sample at 40.02% concentration of resin is thehighest of all the experiments. The yield at 4.81% of feedstock is amongthe highest within this set of screening experiments. The percentage ofrubber in the extract is reported at 1.72% of the feedstock but issurpassed by several other experiments.

These process conditions indicate that the presence of acetone promotesthe extraction of resin. These process conditions should be consideredas a single step in a two-step process for extracting resin and rubberseparately and sequentially. Using the ASE method, the residue has a2.9% concentration of resin, and a 6.5% concentration of rubber.

Example 15 50 ml Extraction with Hexane Co-Solvent, (5,000 psi, 60° C.)

16.12 g of guayule shrub feedstock is placed in an extraction vessel andextracted with carbon dioxide and 15 g of hexane co-solvent at apressure of 5,000 psi and a temperature of 60° C. The flow rate is 3liters/minute. The time of extraction is forty-five minutes. 0.53 g ofsolid yellow material and dark green film is extracted (3.28% offeedstock). Supercritical carbon dioxide at these processing conditionsshows very good selectivity for resins. The extract sample at 34.69%concentration of resin is among the highest of the experiments; however,the yield at 3.28% of feedstock is not as high as several otherexperiments.

The percentage of rubber in the extract is reported at 1.09% of thefeedstock, which is relatively low, showing the rubber is still notextracted in great quantity, utilizing these particular processconditions. These process conditions indicate that the presence ofrelatively low concentration of hexane co-solvent appears to promote theextraction of resin and slightly promote the extraction of rubber. Theseprocess conditions should be considered as a single step in a two-stepprocess for extracting resin and rubber separately and sequentially.Using the ASE method, the residue has a 2.9% concentration of resin anda 5.3% concentration of rubber.

Therefore, the present method of using supercritical carbon dioxideeliminates or greatly decreases the use of organic solvents which areozone depleting and environmentally unfriendly, while providing a moreeffective method of separating, fractionating and purifying rubber andresins from plant materials.

Various embodiments of the invention are described above in the DetailedDescription. While these descriptions directly describe the aboveembodiments, it is understood that those skilled in the art may conceivemodifications and/or variations to the specific embodiments shown anddescribed herein. Any such modifications or variations that fall withinthe purview of this description are intended to be included therein aswell. Unless specifically noted, it is the intention of the inventorthat the words and phrases in the specification and claims be given theordinary and accustomed meanings to those of ordinary skill in theapplicable art(s).

The foregoing description of a preferred embodiment and best mode of theinvention known to the applicant at this time of filing the applicationhas been presented and is intended for the purposes of illustration anddescription. It is not intended to be exhaustive or limit the inventionto the precise form disclosed and many modifications and variations arepossible in the light of the above teachings. The embodiment was chosenand described in order to best explain the principles of the inventionand its practical application and to enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated.Therefore, it is intended that the invention not be limited to theparticular embodiments disclosed for carrying out this invention, butthat the invention will include all embodiments falling within the scopeof the appended claims.

1. A method for removing rubber and resin from plant material,comprising: preparing the plant material for supercritical extraction;extracting resins from the plant material using supercritical solventextraction; and extracting rubber from the plant material using aco-solvent.
 2. The method of claim 1, wherein preparing the plantmaterial includes pre-treating the plant material.
 3. The method ofclaim 1, wherein the plant material is selected from a group consistingof virgin feedstock, bagasse and previously-extracted plant material. 4.The method of claim 1, wherein the plant material is derived from anon-Hevea plant.
 5. The method of claim 1, where in the plaint materialis guayule.
 6. The method of claim 1, wherein the solvent used in thesupercritical extraction of the resin is a polar solvent.
 7. The methodof claim 1, wherein the co-solvent is a non-polar solvent.
 8. The methodof claim 1, wherein the co-solvent is hexane.
 9. The method of claim 1,wherein the co-solvent is iso-octane.
 10. The method of claim 1, whereinthe co-solvent is cyclohexane.
 11. The method of claim 1, wherein theco-solvent is water.
 12. The method of claim 1, wherein the co-solventis ethanol.
 13. The method of claim 1, wherein the co-solvent isacetone.
 14. A commercial accelerated solvent extraction process,comprising: mixing a sample of plant material with sand; centrifugingthe mixture according to a pre-determined protocol; rinsing the mixturewith a polar solvent, wherein the polar solvent is capable of producinga polar solvent extract; and rinsing the mixture with a non-polarsolvent, wherein the non-polar solvent is capable of producing anon-polar solvent extract.
 15. The method of claim 10, furthercomprising drying the polar solvent extract and the non-polar solventextract.
 16. An apparatus for selectively extracting a biopolymer fromplant materials, comprising: an extraction vessel, wherein theextraction vessel is capable of maintaining a solvent at a supercriticalpressure and temperature; a cylinder, fluidly coupled to the pressurevessel, wherein the cylinder is capable of holding a supercriticalsolution; and a bed of ground plant material, fluidly coupled to thecylinder, wherein the bed is capable of extracting the biopolymer fromthe supercritical solution.
 17. The apparatus of claim 16, wherein theplant material is derived from a non-Hevea plant.
 18. The apparatus ofclaim 16, wherein the plant material is guayule.
 19. The apparatus ofclaim 16, wherein the biopolymer is a non-resin biopolymer.
 20. Theapparatus of claim 19, wherein the non-resin biopolymer is rubber. 21.The apparatus of claim 16, wherein the bed is further capable ofextracting a resin from the supercritical solution.